Controlling Invasive Species (CIE A Level Biology)

• A species that has moved into an ecosystem where it was previously unknown is an invasive species
• An invasive species can occur naturally as a result of a species migrating or expanding their habitat but most recorded incidents of invasive species have been caused by humans
• In the past humans have:
  • Knowingly collected and traded species between countries via ships
  • Unknowingly provided transport for invasive species to a new ecosystem
  • Introduced alien species deliberately as biological control for pests

• Japanese knotweed (Reynoutria japonica) is the UK’s most invasive non-native plant species
  • There are several natural population controls that exist for Japanese knotweed in its natural habitat in Japan
  • The irregular climate and the deposits of volcanic ash over the ground limit its growth
  • A German botanist brought the plant to the UK in the 19th century because he admired its beauty
  • Because the UK does not possess the same environmental factors the plant was able to grow unchecked
  • Since the 1800s it has spread across the UK and become a major problem
  • It grows at a rapid rate, with its strong roots breaking up tarmac and blocking out all sunlight for the native plant species

Problems with invasive alien species

• The biological process of evolution often brings balance to an ecosystem
• Through evolution the environment a species lives in strongly influences the adaptations that the species evolve to live in that environment
• A non-native invasive species will have evolved adaptations for survival in different environmental conditions so when they are introduced into the new ecosystem this can upset the balance
• In a new ecosystem invasive species will have few or none of the natural population controls that existed in their previous ecosystem:
  • They will have no natural predators or competitors

• As a result they are able to increase in number at a rapid rate
• This can affect the processes within an ecosystem
  • Competition may occur between invasive species and native species that occupy a similar niche with the native species getting displaced or pushed to extinction. It could be competition for things such as prey, soil nutrients, light and space
  • Many invasive species can be over successful predators causing a massive decline in their prey species
  • Invasive species can introduce new diseases, to which the native species have no natural immunity
  • The biodiversity of an ecosystem is impacted which reduces its productivity

• Humans can also feel the knock-on effects of an invasive species taking over an ecosystem
  • The spread of novel diseases and irritants of the skin / breathing system directly affect human health
  • The economy of a country can be severely impacted by the costs of trying to control invasive species and their negative effects
  • In the past travel has been brought to a standstill by invasive species, with some plant species prone to blocking up waterways

The Cane Toad in Australia

In the early 1900s, there was a major problem with the sugarcane crop in Australia. An insect pest was destroying the crop and causing major economic losses for many farmers. It was decided that the non-native cane toad (from Hawaii) should be introduced so that it could act as a biological control. After a short period of time the numbers of cane toads increased rapidly due to a lack of natural predators and they spread into other habitats outside of the sugarcane plantations. This had a knock on effect on other species:

• The cane toad is toxic when eaten
• The northern quoll, which is an endangered marsupial carnivore, declined steeply in numbers as they preyed on the cane toad
• Other amphibian species face increased competition for food and resources
• The eggs of ground-nesting birds are often eaten by cane toads

The cane toad (Bufo marinus)

Charles J. Sharp, CC BY-SA 4.0, via Wikimedia Commons